Breivik "took one capsule" at around noon at a dose about 50 percent stronger than what is approved under European Union regulations, Moerland told the court, according to Norway's TV2. There were also traces of anabolic steroids in Breivik's system, he added.

Moerland said large doses of ephedrine could lead to temporary psychosis or confusion as it can mimic the effects of amphetamine.

Anabolic steroids may have factored into the 33-year-old's aggressive behavior, Moerland said. There have been numerous studies that correlate steroid usage with increased aggression and violence, with media reports coining the term "roid rage" to describe the side effect.

Breivik in his longwinded manifesto described that he used anabolic steroids for several weeks before the massacre and also admitted to using ECA stacks, TV2 reported.